Researchers have documented much of his career. Box scores reveal 235 wins and 84 losses and a winning percentage of .737. He also notched 3,832 strikeouts, an ERA of 1.37 and 86 shutouts against all levels of competition. He completed 296 of 322 starts (92%), had 22 one-hitters, six no-hitters and a perfect game. He also had a 30 strikeout game, 26 games with more than 20 strikeouts and a total of 166 double digit strikeout games. Donaldson could also hit, batting .334 in over 1,800 at bats.
During Donaldson’s 1915 season, he struck out an average of 18 batters a game and fanned 30 in a marathon 18-inning contest. Donaldson not only struck out more than 500 batters that year, but did it three years straight. Most of his accomplishments were against semi-professional competition, but Donaldson also did very well in his relatively few contests against highest level professional baseball teams, and there were a number of first-person reports of his talent from such opposing managers and players.
His championship club eventually disbanded, but after World War I, many of its players were signed by J. L. Wilkinson for the newly-formed Kansas City Monarchs in 1920. Donaldson played part-time with the Monarchs through much of the 1920s, also working with various semi-pro barnstorming teams in Minnesota. Crowds of over 5,000 people sometimes watched these exhibition games in the mid-1920s.
In 1923, he formed his own team of all-stars, the Donaldson Stars (though frequently referred to as the All-Nations), to play exhibition games against local baseball clubs throughout the Midwest, especially in such Minnesota towns as Bertha, Lismore and St. Cloud.
Donaldson made a comfortable living traveling through rural America, even during the Depression. Like many black barnstormers of the time, Donaldson faced white major leaguers and fared well enough to prompt New York Giants manager John McGraw to say, "I think he is the greatest I have ever seen." McGraw is also alleged to have said about Donaldson: "If I could dunk him in calamine lotion, I'd sign him."
Perhaps most impressive, Donaldson traversed towns in Minnesota to play ball, sometimes as the only black player on a small-town semipro team, at a time when the Ku Klux Klan was active in the state. Three years after the notorious lynchings of three black circus workers in 1920 in Duluth, Minnesota, Donaldson led a barnstorming troupe into Duluth, where he pitched and beat a team of white all-stars from the Iron Range, 6-3.
Donaldson's charisma, composure and stellar character were a countermeasure to the deep-seated prejudices of the time, baseball historian Pete Gorton has said. "But I don't want anyone to look at the career of John Donaldson and think 'Oh, here's another poor black ball player exploited by the "Man" or by the times he lived,'" the writer noted. "This is a story of a man who was covered by the media and adored by the fans and had an outstanding career on the baseball diamond."
After more than twenty years as a player, Donaldson retired in 1934. Settling in Chicago, he worked for the U.S. Postal Service. Although Donaldson never gained the full recognition for his pitching skills during his lifetime and was never admitted into major-league baseball during his career, he made history by becoming the first full-time black talent scout in the big leagues for the Chicago White Sox of the American League in 1949.
Research also suggests that Satchel Paige owes much of his style and form to Donaldson, Paige's pitching coach during the 1930s.
Elden Auker, a former major league pitcher, who had played against Donaldson, related this anecdote when he (Auker) was 95 years old in 2006: "I played against Donaldson in 1929. I was in college and we played at an Arapaho Indian reservation in Kansas. I pitched against Paige and I won, 2-1. Donaldson played center field. Donaldson got out in center field and squatted like a catcher," Auker related. "The Monarchs had a catcher named Young, and he squatted behind home plate and they played catch from 300 feet. They threw the ball on a line. If I hadn't seen it, I wouldn't have believed it."
At age 60, Donaldson was voted a first-team member of the renowned 1952 Pittsburgh Courier player-voted poll of the Negro Leagues best players ever.
Donaldson died at age 78 in Chicago and is buried in Burr Oak Cemetery in Alsip, Illinois. He was buried in an unmarked grave at the cemetery, until Peoria, Illinois anesthesiologist Jeremy Krock raised enough money for a proper headstone.
Donaldson was nominated for a special ballot of pre-Negro leagues candidates for inclusion in baseball's Hall of Fame. A 12-member voting committee, appointed by the Board of Directors and chaired by former Major League Baseball Commissioner Fay Vincent, however, did not choose Donaldson for membership in the Hall of Fame in Cooperstown in February 2006.